This application is the national phase under 35 U.S.C. xc2xa7371 of prior PCT International Application No. PCT/NO97/00067 which has an International filing date of Mar. 6, 1997 which designated the United States of America, the entire contents of which are hereby incorporated by reference.
The invention concerns a method for optical data storage in an optical data memory which comprises data-carrying media in the form of sheets, foils, tapes, cards and disks, either separately or in combination, wherein data is stored in one or more data-carrying layers or volumes in the data-carrying medium/media and written and/or read by means of light, and wherein there is employed in the method of a write/read device with a first optical lens system and one or more light sources provided in optical relation to said first optical lens system. The invention is also directed to a method for positioning of an optical data-carrying medium for optical data storage in an optical data memory which comprises data-carrying media in the form of sheets, foils, tapes, cards and disks, either separately or in combination, wherein data is stored in one or more light-sensitive data-carrying layers or volumes in the data-carrying medium/media and written and/or read by means of light, and wherein there is employed in the method a write/read device with a first optical lens system associated with one or more light sources provided in optical relation to the first optical lens system, such that the first optical lens system is assigned to the data-carrying medium and directs light from the light source or light sources thereto. The invention is also directed to a method for localizing data stored in or written into an optical data memory which comprises data-carrying media in the form of sheets, foils, tapes, cards and disks, either separately or in combination, wherein data is written and/or read by means of light, wherein there is employed in the method a write/read device with a first optical lens system and one or more light sources provided in optical relation to the first lens system, and wherein for storage or writing a method is employed. The scope of the invention is specified solely in one of the claims which are, in part, directed to a device for implementing the method for the optical data storage and the method for localizing data stored in or written into an optical data memory, wherein the device comprises a write/read device.
In general the present invention concerns methods and devices for optical storable and retrieval of data in planar data media or data carriers in the for cards, disks or tapes. Similarly, the invention also concerns the mechanical construction and procedures for mechanical handling and control of the data-carrying medium during write and read operations.
Medium-high density optical data storage today is totally dominated by laser-based tracking systems, in which a sharply focused light beam follows a data track under servocontrol. e.g. in a spiral pattern covering the surface of the rotating disk. This method has a number of serious drawbacks. First of all a high precision optomechanical system is required with attendant cost and space constraints. Secondly, reading is performed serially thus restricting the opportunities for sophisticated error correction by correlation and adaptation based on synoptic raw data acquisition from the data-carrying medium. Furthermore, very fast random access is impossible due to the mechanical tracking and finally it is difficult or impossible to increase the data density in the write/read speeds by multi-level data encoding at each individual datum location.
Recently a radically different concept has been proposed, based on incorporating a large number of microlenses in the actual data carrier and addressing a cluster of data spots under each microlenses by illumination of the microlenses from a predefined set of incidence angles, as described in Norwegian patent application no. 90 0443 with the title xe2x80x9cData storage medium and methods for input and output of data.xe2x80x9d The data spots are located in a thin bum film inside the data-carrying medium, thus causing light which is incident on the microlenses from the write/read device to be focused to a series of small spots in the burn film, one spot being assigned to each microlenses. The microlenses act as magnifying glasses, increasing the apparent size of each data spot in the burn film by one order of magnitude or more and making it possible for read-out to be performed by simultaneous imaging of large areas on the data-carrying medium, since the depth of field increases as the square of the resolution. The use of an electronic matrix detector, such as a CCD camera for the imaging enables the imaged data spot pattern to be subjected to logic operations which completely eliminate the need for mechanical alignment and tracking. In addition to this, the integration of microlenses and a data-carrying medium provides a number of other advantages. Unfortunately this is only in theory. For practical implementation in a commercial environment, there exists a number of technological as well as cost-related barriers: A major problem is that of mass production of data-carrying media with integrated microlenses, since in order to fully exploit the potential with regard to high data densities, each microlenses must be very precisely controlled with respect to physical shape, positioning relative to the burn film and bulk optical properties. Each individual data-carrying medium, such as a card or disk, typically has to incorporate hundreds of thousands or millions of microlenses, arranged in precisely defined patterns parallel to the data-carrying surface.
As a further example of prior art when using microlenses or lenslets in data-carrying medium, U.S. Pat. No. 4,663,445 (Sprague) may be mentioned, wherein the writing to a memory medium takes place sequentially with a scanning beam and reading takes place in parallel from a matrix of light sources, U.S. Pat. No. 3,902,788 (Strehlow) wherein lenslet matrixes are provided on each side of the memory medium and respectively applied to writing and reading, and International published patent application WO93/13529 (Russell) which discloses a random access optical memory wherein the data-carrying medium with integrated lenslets in some embodiments are in the form of data cards or data tapes which are introduced in a write/read device and position in relation thereto, the positioning taking place by means of spring mechanisms and reference surfaces in order to position data fields, for instance in relation to the detector used for reading.
Further known from U.S. Pat. No. 5,483,511 (Jewell et al.) is an optical memory system which employs a plurality of optical write/read beams from semiconductor layers for simultaneous writing or reading of information to a plurality of tracks in a moveable storage medium. A matrix of lasers for writing provided vertically relative to the data-carrying medium is used with an assigned matrix of microlenses in order to reduce the divergence of each laser beam and correspondingly another microlenses matrix is used for focusing the beams to a light spot on the detector matrix, possibly accompanied by compensation for field curvature. Essentially the data carrying medium or the memory medium in this case are a rotating disk, for instance of the CD-type, with spiral tracks or a moveable data type with parallel tracks. For deflection respectively to and from a memory medium and focusing thereto a relatively complicated data system with lenses, mirror and beam splitter is used.
At present a number of techniques are under development which are intend to be employed to create arrays of microlenses which are formed in situ by deposition, transformation, etching, etc. However, the current state of the this field is not such that quality size and cost parameters can simultaneously satisfy the demands for mass-produced data-carrying media suitable for consumer applications.
As an alternative to in situ solutions the use has been proposed of transparent microspheres which are mounted in regular arrays on a surface. The only known, possible source of microspheres with technical specifications which could satisfy the requirements of data-carrying media with integrated microlenses is presently Dyno Particles AS of Lillestrom, Norway, who employs a proprietary technique, known as the Ugelstad process for production of polymer microspheres in sizes restricted to 100 microns or less. In addition to the purely technical problems regarding the quality and uniformity of the microspheres themselves, the commercial viability of using microsphere-based, data-carrying media is dependent on resolving price and delivery issues stemming from the single-source situation, and these problems may well persist beyond the lifetimes of the patent protection of the method for manufacturing such microspheres according to the Ugelstad method. Even though perfectly smooth, round, clear and monosized polymer microspheres can be obtained in bulk at acceptable prices, a number of problems will still remain. These include the fact that the spheres have to be positioned on and integrated in the data-carrying medium at a commercially acceptable yield, acceptable speed and reasonable costs. This normally involves production lines which each supply a data carrier containing millions of microspheres every few seconds. Moreover, the spherical focusing surface creates imaging errors which limit the attainable spot size, especially at large apertures where spherical aberration is a serious problem. In addition, the Ugelstad process or the so-called xe2x80x9cSwollen Emulsionxe2x80x9d process limits the choice of optical materials for the microspheres. Thus the refractive index is typically in the range of N=1.5 to N=1.6, i.e. it is significantly less than for other polymer and glass optical materials which are currently in general use. A high microlenses index of refraction is therefore a significant factor in achieving small focal spot sizes and thereby high data storage densities.
The object of the present invention is to provide remedies for the shortcomings and difficulties inherent in the state of the art as set forth above. This applies both to mainstream technologies based on tracking laser beams and relative to integrated microlenses technology, and a particular object is to deal with isolated technical issues in connection with such technologies as well as potential barriers to their commercial exploitation.
This object is achieved according to the present invention with a method which is characterized by forming the first optical lens system from a number of lenslets arranging the lenslets in an arraylike configuration of lenslets such that the lenslets form a predetermined, freely chosen pattern, positioning the data-carrying medium such that each lenslet is assigned to one or more areas on one of the respective data-carrying media of the optical data memory, and directing light from the light source or light sources through the optical lens system, such that each lenslet directs the light to the respective area(s) associated with it on the data-carrying medium. This object is further achieved by a method which is characterized by positioning the data-carrying medium on at least one reference surface, the position of the data-carrying medium being maintained through at least one cycle which comprises writing and reading respectively or only reading of data in the data-carrying medium. This object is also achieved in part by a method which is characterized in that in a first stage it comprises bringing the data-carrying medium to register with the first optical lens system in the write/read device by means of a translational and/or rotational movement generated by mechanical servos which in engagement with the data-carrying medium are controlled by a deviation minimizing program, and in a second stage allowing light from the write/read device to pass through a discrete or continuous set of angular coordinates which are located near one or more sets of reference angular coordinates, the optical response from the data-carrying medium being detected simultaneously and in parallel by means of the write/read device as a predetermined set of x,y coordinates, with subsequent generation of angle correction data for all x,y coordinates; together with a device which is characterized in that there are provided integral with the write/read device a first optical system consisting of an array of lenslets, one or more light sources arranged to illuminate the lenslets individually or in parallel and with predetermined illumination parameters, with the result that light from the lenslets is directed toward specific areas on a data-carrying medium inserted in the device, a second optical system arranged for imaging of the illuminated data-carrying medium and an electronic matrix detector with a light-sensitive elements arranged in a one- or two-dimensional pattern for recording the illuminated data-carrying medium, and that the write/read device is further connected to a logic unit arranged for analysis of the recorded image emitted in the form of signals from the electronic matrix detector.
Further features and advantages are presented in the attached dependent claims.